The goal of our work is to understand sound transmission in normal, diseased and reconstructed middle ears so as to develop better diagnostic tests and surgical procedures for patients with middle-ear disease. Middle ear diseases, such as chronic otitis media (COM), which affect over 10 million people in the U.S., are common causes of significant conductive hearing loss that range in severity up to 60 dB. Hearing losses of 30-60 dB have significant adverse effects on patients' lives and their ability to communicate. It is acknowledged by otologic surgeons that postoperative hearing results after tympanoplasty procedures for COM are often unsatisfactory. Factors contributingto failures after surgical procedures include lack of clear understanding of structure-function relationshipsin the reconstructed ear and failure of current diagnostic tests (otoscopy,audiometry, tympanometry) to identify such relationships. Over the past five years, we have utilized a unique and powerful combination of methods to study middle-ear mechanics including in-vlvo measurements using laser Doppler vibrometry, In-vltro measurements in cadaveric human temporal bones, and physics-based, quantitativemodeling. Our work has a) resulted in new tests employing laser vibrometry for improved preoperative differential diagnosis of ossicular lesions in patients with an intact tympanic membrane, and b) provided specific surgical recommendations to optimize postoperative hearing results in certain types of middle-ear surgical procedures (examples: type III tympanoplasty, stapedectomy). Over the next five years, we aim to develop and exploit these methods further in a) normal ears, b) diseased ears with tympanic membrane perforations and superior canal dehiscence, and c) ears that have undergone ossicular or tympanic membrane reconstructions for COM. We will also perform in-vitro evaluation of a novel, hand-held probe for objective, intra-operativediagnosis of ossicular fixation. We anticipate that our work will lead to better understandingof structure-function relationships in normal and pathological middle ears, improved differential diagnosis of conductive hearing loss, better preoperative patient counseling and surgical planning, reduction in the number of failed surgeries and optimization of surgical techniques and hearing results.